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Last week, I
attended a science and stewardship conference of The Nature Conservancy in
Madison, Wisconsin. It was an inspiring
and thought-provoking week. There were a
lot of topics that will provide fodder for future blog posts, but I wanted to
start with an issue that came up in several sessions. The topic had to do with setting appropriate
objectives for conservation strategies, and for land management in
particular. In short, it’s really
important to make sure we’re not setting objectives that are focused on
strategies rather than outcomes.

This mixed-grass prairie is managed with both prescribed fire and grazing. However, neither fire nor grazing is the objective, they are tools that are strategically employed to create desired outcomes. Gjerloff Prairie – Prairie Plains Resource Institute

Here’s an
illustration of what I mean. If I was
planning a vacation for next summer, I probably wouldn’t start with the
following question: “What mode of transportation should I take on my vacation
next year?”

Clearly, it’s tough to answer that question without knowing more about the ultimate objectives of the vacation. Where do I want to go? What time of year am I going? How many people are going with me? If I’m planning to travel from Nebraska to Ireland, I probably won’t be able to do that by bus. I could conceivably travel by motorcycle (if I had one) to the Rocky Mountains, but probably not if I was going during the winter or planning to take little kids with me.

It seems
silly to start by thinking about how to get somewhere before deciding where to
go, but as land managers, it’s easy to fall into exactly that mindset. We sometimes set objectives about using fire
or grazing, for example, instead of first defining the outcome we want and then
thinking about what tools and strategies might get us there (which may or may
not include fire or grazing). In this
post, I’ve provided examples of how this trap can present itself, both to
managers of conservation land and private landowners, and some thoughts about
how to avoid the trap.

Significant
research has helped us understand the kinds of fire and grazing patterns under
which North American prairies developed.
For example, in many places, we have a pretty good idea how often a particular
site burned, on average, before European settlement. We also have reasonably good information on
the presence, abundance, and behavior of historic grazers. Based on that information, a land manager
could decide that the best management for their prairie would be to reinstate,
as closely as possible, the timing and intensity of historic fire and grazing
that site likely evolved under.

Historically, prairies in this region probably burned on an average of every 4-5 years. However, within that average range, there would have been wide variation. More importantly, this prairie sits within a very different landscape today, with challenges not faced by those historic prairies.

Patch-burn grazing is often described, for example, as “mimicking historic fire and grazing patterns.” Mob grazing advocates trumpet (though I’m skeptical) that their system replicates the way bison moved across a landscape. Some in the Upper Midwest region of North America point to research showing high populations of indigenous people and scarce evidence of abundant bison and argue that their prairies should be managed only with fire. We can argue about all three of those examples – and many more – but the bigger point is that none of those arguments should determine our management strategies. Again, we shouldn’t be setting objectives about the strategy we want to use without first identifying the outcome we want.

To make a
clunky return to my vacation travel analogy, it would be silly of me to choose
horseback as my preferred mode of transportation across the Great Plains to the
Rocky Mountains just because it’s what worked several hundred years ago. Today’s landscape is broken up into countless
fenced off private land parcels, which would make cross-country horse travel
difficult, to say the least. In
addition, there is a pretty nice set of modern opportunities (roads and vehicles)
I can take advantage of nowadays.

Likewise, our prairies exist within a different world today, with a new set of challenges and opportunities. Mimicking historic disturbance regimes won’t necessarily keep prairies in good shape in a world with habitat fragmentation, massive invasive species pressure, climate change, nitrogen deposition, and other factors. And speaking of good shape, our first and primary concern should really be to define what “good shape” is, right? Are we managing for plant diversity or a few rare plants? Are we trying to sustain diverse bird populations? Habitat heterogeneity? Is ecological resilience the goal? If so, what are the factors driving resilience, and how to we sustain those? There are countless reasonable goals for land managers to choose from, many dependent upon scale, but those goals should be based on the outcome we want.

This annually-hayed prairie maintains high plant diversity but provides only one type of habitat structure for nesting birds and other wildlife species. Depending upon the objectives for the site, that could be fine, but it very much depends upon what the manager wants to accomplish.

I feel it’s important to say this here: I am a big proponent of both fire and grazing as management tools – you can find myriad examples of that by searching through my previous blog posts. However, while I think combining fire and grazing can create some fantastic results, those strategies/results don’t fit all objectives. More importantly, your particular site may or may not respond well to those kinds of fire and grazing combinations.

Let’s say
your primary objective is to provide habitat for as many species of grassland
birds as possible. First, you’ll need a
pretty big swath of land – many bird species have minimum habitat size
requirements. Assuming you’ve got
sufficient land, the major factor grassland nesting birds respond to is habitat
structure. Some birds prefer tall thatchy
structure, others like short/sparse vegetation, and others want something
in-between. A reasonable outcome-based
objective might be that you want to provide all three of those habitat types
across your prairie each year (and you’ll want to make sure the habitat are
being successfully used by a diverse bird community). Perfect.
Now, how will you create those habitat types?

Grasshopper sparrows tend to nest in prairies with relatively short structure, but with some thatch (which they use to build nests) along the ground. Some of the highest abundances of grasshopper sparrows around here are found in relatively heavily-grazed prairie.

Fall or
spring fires can create short habitat structure that some birds really like to
nest in. However, some bird species
(e.g., grasshopper sparrows) usually like short habitat with a little more
thatch in the ground layer than is usually found in recently burned
prairies. Also, while burned areas are
short and unburned areas are tall, it’s difficult to create in-between
height/density habitats using only fire.
This is where other tools such as mowing and grazing might be
helpful. Mowing can reduce the height of
tall vegetation and create short or mid-height structure that grasshopper
sparrows, meadowlarks, and other species prefer. Grazing can do the same and can have the advantage
that cattle or bison are selective grazers, eating some plants and leaving
others. This can create structure with
both tall and short vegetation mixed together and can also help suppress
grasses and allow for greater expression of forbs (broadleaf plants) –
something birds such as dickcissels often prefer.

Upland sandpipers prefer to nest where vegetation structure is short, but often move to sites with strong forb cover and a little patchier structure when their chicks become active.

If we’re
trying to create optimal bird habitat, then, fire, mowing and grazing might all
be useful tools to consider. It’s
important to understand how each tool can be used to affect habitat structure,
as well as the potential risks of using each (fire can sometimes kill
aboveground animals and stimulate invasive plants, grazers can sometimes target
vulnerable plants and create issues via trampling). With all of that information, you can start putting
together strategies that employ the right tools, and then test those strategies
against the OUTCOMES you desire. Notice
that the process I’ve just described is independent of the kinds of historic
fire returns for your area or whether or not you think grazing was a significant
factor in the evolution of regional plant communities. Define your objective by the outcomes you
want and test/adapt strategies based on that objective.

Other examples:
At my family prairie, we aren’t using prescribed fire because we’ve been able
to use grazing to meet our objectives of habitat heterogeneity and increasing
plant diversity, and we use loppers/herbicide to successfully control woody
invasion. In small prairies where
preserving particular plant species is the objective, a strategy using only
fire or mowing could be most appropriate.
If that small prairie has rare insects or reptiles that are especially
vulnerable to fire, maybe mowing is the best tool. Regardless, the right tools and strategies
depend upon the outcome-based objective.

This photo was taken in the burned patch of a patch-burn grazed prairie at Konza prairie, near Manhattan, Kansas. The grazing created varied habitat structure because of the selective grazing by cattle. Leadplant and other ungrazed forbs contrast with surrounding short grasses.

For ranchers
and farmers who manage prairies, this same objective setting process should
apply, but of course those prairies also have to help provide sufficient income
to keep a family or business thriving.
Even in those cases, however, it’s still important to start with
outcome-based objectives. Those
objectives can include a certain amount of needed income but should also include
specific habitat or other ecological objectives. Once you’ve decided, for example, that you
really want to manage in a way that provides a certain amount of quail habitat
or provides consistent pollinator resources through the season, you can look
for ways to accomplish that while still providing the needed income. When a conflict between income and habitat
objectives arises, you can make the decisions that make sense to you, but at
least you’re making those decisions with all the information needed to fully
consider the options.

Prescribed fire can be a great tool for accomplishing some objectives, but it can also be difficult to implement for some managers. While it is an important ecological process in prairies, employing prescribed fire should still be seen as a tool/strategy, rather than as an objective in and of itself.

There are
plenty of reasonable prairie management objectives to choose from, but they
should be based on outcomes rather than on tools and strategies. Employing more frequent prescribed fire is
not a good objective. However, using
more frequent prescribed fire might be a great strategy to reach a particular
outcome. (It could also be a terrible
strategy, depending upon your objective.)
Don’t fall into the trap of choosing your transportation method before
you know where you want to go.

P.S. I’m sure some of you are thinking it, so let me address what might appear to be a weakness of my vacation transportation analogy. Yes, it’s perfectly fine to start vacation planning by deciding that you want to take a cruise ship or motorcycle if the OUTCOME you really want is to ride on a ship or motorcycle. If you don’t care where you go, the destination isn’t the outcome, it’s just a by-product of your mode of travel. Fine. But I think you understand what I was trying to say, right? Sure, you could argue that conducting prescribed fires could be your objective if all you want is a legal way to light things on fire and watch them burn. If that’s your objective, though, you’re not managing prairies, you’re lighting things on fire – and there’s a big difference. Ok? Ok.

One of the biggest jobs of a prairie steward is to manage the competition between plants, ensuring that no species becomes too dominant and no species is pushed out of the community. In our prairies, much of our effort is directed toward some of the stronger grass species, including big bluestem, indiangrass, smooth brome, and Kentucky bluegrass. Left unchecked, those grasses (and a few others) can monopolize both light and soil resources and reduce plant diversity. Our management targets those grasses with fire and grazing, often using season-long defoliation by cattle or bison to weaken the competitive ability of those grasses, opening up space and resources for other plants to flourish. Our long-term plant data show that we’ve been able to maintain species richness and a full complement of plant species with this kind of management.

When those major grasses are weakened, one of the most obvious responses is a flush of “weedy” vegetation that quickly takes advantage of the soil and light resources that have become available. Research has shown that growing season defoliation temporarily causes grasses to abandon some of their roots (until defoliation stops and the grasses recover), opening up space for nearby plants to grow larger and more abundant. However, there are still many questions about the actual physical responses of grass roots to defoliation, and gaining a better understanding of that could be really important to prairie managers. Researchers at Kansas State University are actively working on those questions right now. Dr. Jesse Nippert, in particular, has done a lot of work on this subject, including some work on prairie shrubs that I wrote about a few years ago.

Last week, a couple of Jesse’s graduate students, Seton Bachle and Marissa Zaricor, were at our Platte River Prairies, collecting data on roots under grazed and ungrazed conditions. In addition, Seton brought along a nifty tool called an air spade, which uses compressed air to dig into prairie soil with enough force to expel soil particles, but not so much that it tears apart the roots of plants (with the exception of the tiny rootlets at the tips). Seton and I started talking about a year ago about the possibility of getting the air spade up here so we can look for visual evidence of grazing impacts to roots. Marissa and Seton are both doing very in-depth (ha!) measurements of plant root responses, but I also wanted to see what’s those roots really look like. The air spade seemed like a great way to do that.

Here is our sampling area, as seen by our drone. The bottom right portion was burned this spring and has been grazed fairly intensively since. The top left portion is unburned and has had very little grazing pressure.

Dust erupts out of the ground as Seton excavates with the air spade.

For this initial trial, we chose a part of the prairie that was burned this spring and was being grazed intensively by cattle as part of our patch-burn grazing management. Abundant rain this year has meant that the cattle aren’t keeping the grasses as short as we’d really like, but we were still able to find some big bluestem plants that have been cropped pretty short. As a comparison, we went across the burn line to part of the prairie that hasn’t had much grazing pressure in recent years and, because it is unburned, hasn’t had much attention from cattle this year either. As a result, we were (ok, Seton was) able to excavate around the roots of big bluestem plants that had been grazed off to just a few inches of leaf height, as well as ungrazed plants with leaves around 12 inches high.

Here is the excavation spot in the burned/grazed patch.

Here is the unburned/ungrazed excavation site.

As Seton started blowing soil away from the roots (and I photographed the process with my camera and our drone), one of the first things that became obvious was the relatively shallow depth of the main root mass. The work of J.E. Weaver and others has shown that prairie plants, including grasses, have some very deep roots. However, more recent work, including that of Jesse Nippert of Kansas State, Dave Wedin at the University of Nebraska, and others, has shown that those grasses don’t appear to actually use those deep roots for much. In fact, grasses tend to concentrate the vast majority of their root masses in the top foot or so of the soil profile, effectively monopolizing most of the moisture and nutrients there. Forbs tend to pull most of their resources from below that, and shrubs work at even greater depths. I’ll write about this more in a future post, but for now, just trust me when I say that this is abundant evidence for this (and many more questions being pursued). Prairie grasses can have deep roots, but it’s the incredible root density at shallow depths that they most rely on, even during drought.

With the air spade, we could pretty easily see that most of the big bluestem roots were in that shallow depth, and only a few extended down below that. However, as Seton pulled out fully-excavated clumps of big bluestem shoots and roots, my initial reaction was one of disappointment. There didn’t seem to be any obvious difference in the density of roots or size of the overall root mass between the grazed and ungrazed plants.

Marissa and Seton examine the roots in the partially excavated grazed site.

Seton examines some of the roots dug out of the burned/grazed site.

My immediate thought was that because these plants had only been exposed to grazing for about a month, maybe there hadn’t been enough time to see changes in their root masses. In addition, it might be that some of the roots were no longer active, but were still connected to the root mass for now. We’ll be repeating this excavation process later in the season, and might see differences then that aren’t yet obvious. In addition, we’ll look at some roots of grasses that were heavily grazed all of last season and see what those look like. Still, I was a little disappointed not to see a bigger visual difference.

However, when Seton and Marissa looked at the roots, they pointed out something I hadn’t initially seen because I was so focused on root length and density. The diameter of most of the roots of the ungrazed bluestem appeared to be considerably larger than those of the grazed plants. We were working with a small sample size, but among all the plants we dug up, that size difference seemed to be pretty consistent.

An ungrazed clump of big bluestem on the left and grazed on the right. You can’t see the length of all the roots in this image (they were similar between plants) but the ungrazed roots are noticeably thicker than the roots of the grazed plant.

Here’s another look at the difference in root thickness between the grazed plants (top) and ungrazed (bottom).

Marissa explained that thicker roots have more carbohydrates stored in them. Plants that have been defoliated, and are trying to regrow shoots, have to pull carbohydrates from their reserves to do so – pulling them out of their roots and putting them into aboveground growth. Whether those roots kind of deflate as the carbohydrates are pulled from them or stressed plants just create skinnier roots is something Marissa and Seton are hoping to learn from their work. Regardless, carbohydrate storage plays into competitive ability. Grasses rely on their storage capacity to fuel growth and withstand further stress, so differences in root diameter could be part of the answer to why grazed grasses are less competitive. Seton and Marissa plan to examine some cross sections of the roots we dug up to see if they can see more under a microscope than we could by just looking at the roots with our naked eye.

Seton and Marissa’s actual scientific explorations will give us much better answers to questions about grazing impacts on grass roots than simply looking at a few samples, but it was fun to see the actual roots themselves. While the differences between grazed and ungrazed plants weren’t as stark as I’d expected, I’m still looking forward to our next effort later this summer – especially because all I have to do is photograph the results of the hard work Marissa and Seton are doing!

If you’re interested, here is a short 1 minute drone video showing the excavation process. You can also check out Seton’s science website here.

Special thank you to the Nebraska Environmental Trust for funding our drone purchase through a PIE (Public Information and Education) minigrant, administered through the Nebraska Academy of Sciences.